Eigenfunctions dynamic correlations

Using Hartree products, a state now appears as a product of two spatial functions and a spin function that is an eigenfunction of 5. Thus the first four states are nonrelativistic closed-shell singlet states the next two are open-shell singlet states, and the remaining eight are triplet states. If this were a nonrelativistic wave function with independent coefficients for each of these states, the wave function would include elements of non-dynamical correlation, for both the singlet and the triplet components (and would be... 

We have already pointed out that the situations in which a single-determinant wave function can be used as a reference for a correlated method are much fewer in relativistic theory than in nonrelativistic theory. We must therefore resort to methods that do not assume a single-determinant reference. Whether we treat dynamical correlation perturbationally or variationally, it is usually the case that we need to obtain eigenfunctions of some A-particle Hamiltonian, and so we turn to Cl methods. 

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